Parton distribution functions (PDFs) are crucial for simulating particle collisions involving hadrons. Under the assumption of isospin symmetry a proton PDF can be transformed into a neutron PDF. QED effects break the symmetry. PDF fitting groups are working to include these QED effects and provide separate PDFs for the nucleons. We analyze the isospin-breaking effects in three such PDF sets. Isospin violation typically starts at about 1% and can increase to 4.5% when energy scale evolution to Q² = 10³ GeV² is applied. Typically, \bar{d}_p ≈ \bar{u}_p > \bar{u}_p ≈ \bar{d}_n is observed. To explore this isospin symmetry in the quark sea, two approaches are tested: swapping only u(x, Q²) and d(x,Q²), and a second version including the swapping of \bar{u} and \bar{d}.

The option to use an isospin-swapped proton PDF in Sherpa is implemented and compared with fitted neutron PDFs for deep inelastic scattering and the Drell-Yan process. Overall, the results show good agreement between the two methods in terms of total cross-sections. The isospin neutron is consistently closer to the fitted neutron than the proton, with some remaining differences explained by PDF analysis, though some unexpected behaviors are noted. Thus, we conclude that isospin swapping performs well in the Sherpa framework for the sets and processes tested for this thesis but it should be investigated further with a larger variety of sets and processes.